JP6108166B2 - Secondary battery electrode - Google Patents

Description

  The present invention relates to an electrode for a secondary battery.

  Conventionally, secondary battery electrodes used in secondary batteries such as lithium ion batteries and nickel metal hydride batteries are obtained by applying a paste-like mixture containing an active material and a binder (binder) onto the current collector foil. It is manufactured by drying (see, for example, Patent Document 1).

  In Patent Document 1, in order to suppress the segregation of the binder in the secondary battery electrode, a binder capturing liquid capable of capturing the binder is applied to the surface of the current collector, and the current collector provided with the binder capturing liquid is applied. A mixture layer (mixture layer) on a current collector (current collector foil) obtained by applying a mixture paste (mixture paste) containing an active material and a binder to the surface of the substrate and drying the paste. An electrode in which is formed is disclosed.

JP 2011-187343 A

  In particular, in the case of an electrode produced by applying a mixture paste to a current collector foil as in Patent Document 1 (hereinafter also referred to as a coated electrode), the active material specific surface area is used to reduce resistance (improve output) as battery performance. If the reaction field is increased by increasing the value, there is a problem that the cycle characteristics (lifetime) deteriorate.

  On the other hand, in the case of an electrode manufactured by powder molding, the electrode structure makes the electrolyte solution permeability, the orientation of the negative electrode active material, and the positive electrode conductive material dispersibility good, so that the resistance can be reduced. However, for example, it has been found that if there is unevenness in the negative electrode weight (unevenness in weight per unit area), the cycle characteristics deteriorate due to this, and the particle fluidity is controlled on the current collector foil to suppress the unevenness in weight per unit area. It is necessary to accurately laminate the granulated particles. That is, in order to accurately stack the granulated particles on the current collector foil, it is necessary to control to improve the particle fluidity. However, the improvement of the particle fluidity tends to impair the adhesion between the particles, and the resistance reduction effect by the powder molding is impaired, resulting in a decrease in battery performance.

  Specifically, if there are unevenness in the electrode mixture layer of the electrode for a lithium ion secondary battery, the reaction does not occur uniformly throughout the electrode during charge / discharge, and reaction concentration occurs in the portion where the basis weight is thin. In the cycle test for evaluating the cycle characteristics of the secondary battery, since this charge / discharge cycle is repeated, lithium deposition occurs mainly in the reaction-concentrated portion (the portion with a small basis weight). For example, there is a concern that lithium released from the positive electrode, which is the counter electrode, cannot be received at a portion where the negative electrode weight is small. That is, a phenomenon occurs in which the capacity ratio, which is the ratio of the negative electrode to the positive electrode, is less than 1.0. Lithium deposition also proceeds due to these phenomena. Therefore, in a cycle test, an electrode manufactured by powder molding is more likely to deteriorate than the coated electrode, which may cause a decrease in capacity retention rate. Thus, in many lithium ion secondary battery characteristics, output and life are often in a trade-off relationship.

  Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide an electrode for a secondary battery that has reduced resistance and improved cycle characteristics.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

That is, in the secondary battery electrode of claim 1,
On the current collector foil, a first mixture layer in which granulated particles formed including at least an active material and a binder are deposited;
And a second mixture layer formed by applying a mixture paste formed by kneading at least an active material, a binder and a solvent to the upper layer of the first mixture layer and drying the mixture.

In the secondary battery electrode according to claim 2,
The basis weight of the first mixture layer is larger than the basis weight of the second mixture layer.

  As effects of the present invention, the following effects can be obtained.

  In claim 1, as the composition of the electrode mixture layer, by forming the lower layer as a powder molding layer, the permeability of the electrolyte, the orientation of the negative electrode active material, and the positive electrode conductive material dispersibility are improved. Reduced. Further, by using the mixture paste layer as the upper layer, it is possible to suppress the unevenness of the electrode weight per unit area as compared with the case of the powder molded single layer, and thus the cycle characteristics are improved.

  In claim 2, by increasing the basis weight by powder molding, the amount of paste applied can be reduced, and the amount of solvent and the drying time accompanying paste application can be reduced.

The figure which showed typically the manufacturing apparatus of the electrode for secondary batteries which concerns on one Embodiment of this invention. The figure which showed the image of the cross-sectional structure of the electrode (electrode sheet) for secondary batteries which concerns on one Embodiment of this invention. The figure which shows the flow of the manufacturing method of the electrode for secondary batteries which concerns on one Embodiment of this invention. The graph which compared initial stage IV resistance in each evaluation battery which concerns on an Example and Comparative Examples 1 and 2. FIG. The graph which compared the capacity | capacitance maintenance factor after a cycle test in each evaluation battery which concerns on an Example and Comparative Examples 1 and 2. FIG.

Next, embodiments of the invention will be described.
The electrode for a secondary battery according to the present embodiment is applicable as an electrode (electrode sheet) included in a nonaqueous electrolyte secondary battery (for example, a lithium ion secondary battery).

  First, a lithium ion secondary battery will be described as an example of a non-aqueous electrolyte secondary battery including the secondary battery electrode according to the present embodiment.

[Nonaqueous electrolyte secondary battery (lithium ion secondary battery)]
A lithium ion secondary battery (not shown) is formed, for example, by accommodating an electrode body including a sheet-like positive electrode (positive electrode sheet) and a negative electrode (negative electrode sheet) in a superimposed or wound state in the battery container. It is configured as a cylindrical battery, a square battery, a laminated battery, or the like. Specifically, a lithium ion secondary battery forms an electrode body by laminating a positive electrode and a negative electrode formed in a sheet shape by overlapping or spirally winding them through a separator. It is manufactured by filling the electrolytic solution in a state where the body is accommodated in the battery housing, and sealing the battery housing. The lithium ion secondary battery manufactured in this manner includes an electrode body including a positive electrode, a negative electrode, a separator, and the like, and a battery container that holds the electrode body, and the electrolyte solution is non-aqueous. An electrolyte is used.

  The positive electrode (positive electrode sheet) forms on the current collector foil an electrode mixture layer containing an electrode material such as a positive electrode active material capable of inserting and extracting lithium ions, a conductive material, a binder (binder), and a thickener. It is a thing. As the positive electrode (positive electrode sheet), the secondary battery electrode according to the present embodiment can be used.

As the positive electrode active material, a positive electrode active material such as a lithium transition metal composite oxide can be used. As the positive electrode active material, for example, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and a lithium transition metal composite oxide in which a part thereof is substituted with another element can be used.

  The conductive material is for ensuring the electrical conductivity of the positive electrode. As the conductive material, carbon material powders such as natural graphite, artificial graphite, acetylene black (AB), and carbon black can be used.

  The negative electrode (negative electrode sheet) has an electrode mixture layer including a negative electrode active material, a binder (binder), and an electrode material such as a thickener that can occlude lithium ions during charging and can be released during discharging. Is formed. As the negative electrode (negative electrode sheet), the secondary battery electrode according to the present embodiment can be used.

  The negative electrode is not particularly limited as long as it can use a negative electrode active material having the characteristics of occluding lithium ions during charging and releasing lithium ions during discharging. Examples of the material having such characteristics include lithium metal, carbon materials such as graphite and amorphous carbon, and the like. Among them, it is preferable to use a carbon material having a relatively large voltage change with charging / discharging of lithium ions, and it is more preferable to use a carbon material made of natural graphite or artificial graphite having high crystallinity.

  The binder (binder) plays a role of binding and bonding the positive electrode active material, the conductive material particles, the negative electrode active material particles, and the like. In addition, the binder plays a role of binding and holding these particles and the current collector foil. As such a binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene copolymer (SBR), a fluorine-containing resin such as fluorine rubber, or a thermoplastic resin such as polypropylene is used. it can.

The thickener is for imparting viscosity to the electrode mixture paste (positive electrode mixture paste or negative electrode mixture paste). As the thickener, for example, polyethylene oxide (PEO), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC) and the like are used.
In addition, a thickener is used when it is desired to give viscosity to the electrode mixture paste, and may be appropriately used as necessary.

  The separator is for electrically insulating the positive electrode and the negative electrode and holding the non-aqueous electrolyte. Examples of the material constituting the separator include a porous synthetic resin film, particularly a porous film such as a polyolefin-based polymer (polyethylene, polypropylene).

Examples of the electrolytic solution include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). A solution in which a lithium salt such as LiPF ₆ , LiClO ₄ , LiBF ₄ or the like is dissolved as a supporting electrolyte in a mixed organic solvent such as a chain carbonate such as can be used.

  The positive electrode (positive electrode sheet) and the negative electrode (negative electrode sheet) described above are overlapped or wound via a separator to form an electrode body, and the positive electrode and the negative electrode terminal communicated to the outside from the positive electrode and the negative electrode. Are electrically connected to each other, and this electrode body is housed in an appropriate battery housing (a metal or resin casing, a bag body made of a metal laminate film such as aluminum), these positive electrodes, and A lithium ion secondary battery is configured by filling a nonaqueous electrolyte between the negative electrodes and sealing the battery housing.

  Next, the manufacturing apparatus 1 for manufacturing the electrode for secondary batteries which concerns on this embodiment is demonstrated using FIG.

  The secondary battery electrode manufacturing apparatus 1 (hereinafter referred to as the manufacturing apparatus 1) according to the present embodiment applies a binder 20 to the current collector foil 2 (binder coating) while conveying the current collector foil 2. Three layers (binder layers) are formed on the current collector foil 2 by continuously performing the four steps of supplying and molding the powder composed of the granulated particles 21, applying the electrode mixture paste 23, and drying the electrode mixture paste 23. 100, an electrode mixture layer 200 (see FIG. 2) comprising a powder molding layer 110 as a first mixture layer and a mixture paste layer 120 as a second mixture layer. As shown in FIG. 1, the manufacturing apparatus 1 is mainly composed of a conveying means 3, a binder applying means 4, a powder molding apparatus 5, a mixture paste applying means 6, and a drying furnace 15 as a drying means. ing.

  The current collector foil 2 is a thin long sheet-like electrode base material used when manufacturing a secondary battery electrode. The current collector foil 2 is a metal foil (for example, an aluminum foil for the positive electrode and a copper foil for the negative electrode) on which the predetermined electrode mixture layer 200 is formed by the manufacturing apparatus 1 on one side surface or both side surfaces (in this embodiment, one side surface). ).

  The conveying means 3 engages the current collecting foil 2 supplied from a supply roller (not shown) provided on the upstream side of the conveying means 3 with a plurality of rollers, and a predetermined conveying speed ( In this embodiment, it is an apparatus for conveying in order to the binder application | coating means 4, the powder shaping | molding apparatus 5, the mixture paste application | coating means 6, and the drying furnace 15 in order of 2 m / min). The conveyance means 3 includes a plurality of guide rollers 3a, 3b, 3c, a backup roller 6a included in the mixture paste application means 6, a supply roller (not shown) as a current collector foil supply unit, and a current collector foil winding It is mainly comprised from the winding roller (not shown) which is a part. The winding roller is provided on the downstream side of the drying furnace 15. As shown in FIG. 1, by setting the current collector foil 2 on the transport means 3, a transport path for the current collector foil 2 is formed. Further, the current collector foil 2 is wound around the supply roller for a predetermined length in advance, and the current collector foil 2 drawn out from the supply roller passes through the plurality of guide rollers 3a, 3b, 3c and the outer peripheral surface of the backup roller 6a. And the current collector foil 2 extended from the backup roller 6 a is wound around the winding roller via the drying furnace 15. Thus, when the take-up roller is driven to rotate at a predetermined speed by a drive means (not shown), the current collector foil 2 wound around the supply roller is drawn out, first conveyed to the binder application means 4, and then guided to the guide roller. It is conveyed to the powder molding device 5 via 3a and 3b, and then conveyed to the mixture paste applying means 6 via the guide roller 3c. The current collector foil 2 is transported while being supported by the outer peripheral surface of the backup roller 6a on the back side, and is transported so as to face the die coater 6b. Then, the current collector foil 2 that has passed through the mixture paste applying means 6 passes through the drying furnace 15 and is taken up by a take-up roller. That is, the conveying means 3 rotates the winding roller by a driving means (not shown), whereby the current collector foil 2 is fed along the conveying path at a predetermined conveying speed at the binder applying means 4, the powder molding apparatus 5, and the mixture. It is possible to convey the paste to the paste applying means 6 and the drying furnace 15 in order.

[Binder application method (gravure coater)]
The binder application unit 4 is provided on the upstream side of the conveying path of the current collector foil 2 in the manufacturing apparatus 1, and the slurry-like binder 20 is applied to one side surface (surface) of the current collector foil 2 with a predetermined basis weight. A gravure coater capable of applying (coating) the binder 20. The binder application unit 4 includes a rotatable pressure roller 7, a gravure roller 8 that is pressure-bonded to the pressure roller 7 via the current collector foil 2, a storage tray 9 that stores the binder 20, and a blade 10. The binder application unit 4 can apply the slurry binder 20 to one side surface (surface) of the current collector foil 2 fed from a supply roller (not shown) by the pressure roller 7 and the gravure roller 8.

  Specifically, a part (lower part) of the gravure roller 8 arranged on the lower side of the current collector foil 2 conveyed along the conveyance path is immersed in the binder 20 in the storage tray 9 and is collected along the conveyance path. It arrange | positions so that a part (lower part) of the press roller 7 arrange | positioned above the electric foil 2 may press the other side surface (back surface) of the current collection foil 2 conveyed along a conveyance path | route. The gravure roller 8 has a so-called predetermined-type gravure pattern on its outer peripheral surface, and the gravure pattern is formed by a predetermined-type engraving. The gravure roller 8 is rotated in a direction opposite to the conveying direction of the current collector foil 2 by a driving unit (not shown). When the gravure roller 8 rotates, the binder 20 in the storage tray 9 adheres to the outer peripheral surface of the gravure roller 8, and the binder 20 attached to the gravure roller 8 is scraped by the blade 10 so that the adhesion amount of the binder 20 becomes a predetermined amount. Be dropped. Then, the gravure roller 8 having a predetermined amount of the binder 20 attached to the outer peripheral surface presses one side surface (the front surface) of the current collector foil 2, whereby the binder 20 is formed on the current collector foil 2 with a predetermined basis weight and predetermined patterning. Application (patterning application) is performed on one side surface. Thus, the binder coating means 4 forms a binder layer (binder coat) 100 on one side surface (surface) of the current collector foil 2. Although details will be described later, in the electrode (electrode sheet) according to the present embodiment, the binder layer 100 formed by the binder application unit 4 is the lowest layer in the electrode mixture layer 200.

[Powder molding equipment]
The powder molding apparatus 5 is provided on the downstream side of the binder application unit 4 in the transport path of the current collecting foil 2 guided by the guide roller 3b and the guide roller 3c, and the current collector transported along the transport path. By continuously supplying granulated particles 21 that are powdered electrode mixture to the foil 2 and press-molding (compression molding) the current collector foil 2 to which the granulated particles 21 are supplied. This is an apparatus for forming a powder molding layer 110 composed of granulated particles 21. As shown in FIG. 1, the powder molding apparatus 5 mainly includes a powder supply apparatus 11, a flattening means (squeegee 12), and a molding means 13.
The granulated particles 21 that are the powdery electrode mixture are granulated by a spray drying apparatus (not shown) described later.
Moreover, although the powder shaping | molding apparatus 5 of this embodiment is a structure provided with the planarization means (squeegee 12), it does not specifically limit to the structure of this embodiment. That is, the flattening means (squeegee 12) in the powder molding apparatus 5 is not an essential component.

  The powder supply device 11 supplies the granulated particles 21 which are powdery electrode mixture onto the current collector foil 2 and forms the supplied granulated particles 21 as a deposited layer on the current collector foil 2. Device (powder feeder). The powder supply device 11 can continuously supply a certain amount of the granulated particles 21 onto the current collector foil 2 and deposit the granulated particles 21 on the current collector foil 2.

  The conveyance means 3 is a means for conveying the current collector foil 2 in order to the powder supply device 11, the squeegee 12, and the molding means 13 in the powder molding apparatus 5. The conveying means 3 can convey the granulated particles 21 supplied from the powder supply device 11 onto the current collector foil 2 to the downstream side by driving a driving means (not shown).

  The squeegee 12 is a blade member that is provided on the downstream side of the powder supply device 11 and has a sharp tip at the tip. The squeegee 12 faces the tip downward and has a predetermined gap between the tip and the surface of the current collector foil 2. The arrangement is fixed so as to have a gap (Gap). The squeegee 12 planarizes the granulated particles 21 supplied onto the current collector foil 2 by the powder supply device 11 and deposits the powdered granulated particles 21 having the same thickness as the predetermined interval. It is a planarization means for forming.

The molding means 13 is a roll-type pressure molding means provided on the downstream side of the squeegee 12, and has a plurality of rotatable press rollers (upper and lower pressure rollers in this embodiment) 13a and 13a. The molding means 13 can be heated and pressurized in the thickness direction of the current collector foil by inserting the current collector foil 2 on which the deposited layer of the granulated particles 21 is formed between the upper and lower press rollers 13a and 13a. A so-called roll press process is possible. Specifically, the molding means 13 holds each of the press rollers 13a and 13a while holding the current collector foil 2 on which the powdery deposited layer made of the granulated particles 21 is formed between the press rollers 13a and 13a. A thickness or density (electrode) is applied to the current collector foil 2 discharged from the downstream side of the molding means 13 by performing a roll press process under predetermined hot press conditions (heating temperature / pressing pressure) while rotating in opposite directions. It is possible to form the powder molding layer 110 having an appropriately adjusted density. Although details will be described later, in the electrode (electrode sheet) according to the present embodiment, the powder molding layer 110 formed by the powder molding apparatus 5 is the lower layer in the electrode mixture layer 200. In this powder molding device 5, powder-like granulated particles 21 are supplied on a binder layer 100 composed of a slurry-like binder 20 applied to the current collector foil 2 by the binder application unit 4, and are rolled. By processing, the powder molding layer 110 is formed on the binder layer 100.
In addition, in the powder molding apparatus 5 of this embodiment, although it is the structure provided with the shaping | molding means 13 (heat press means), it does not specifically limit to the structure of this embodiment. That is, the molding means 13 (heat press means) in the powder molding apparatus 5 is not an essential configuration.

[Paste application method]
The mixture paste coating means 6 is a paste-like paste containing an electrode active material, a binder, a solvent, etc. on a powder molding layer 110 (lower layer) made of powdered granulated particles 21 containing an electrode active material and a binder. This is means for applying an electrode mixture paste 23 which is an electrode mixture. As shown in FIG. 1, the mixture paste application unit 6 is mainly composed of a backup roll 6a, a die coater 6b, a pump 6c, and a tank 6d.
In addition, although the mixture paste application | coating means 6 of this embodiment is a structure provided with the die coater 6b, it is not limited to the structure of this embodiment in particular. That is, the mixture paste applying means 6
The die coater 6b in FIG.

  The backup roll 6a is a roller that is disposed to face the die coater 6b and supports the other surface side (back surface) of the current collector foil 2. The die coater 6 b has a discharge port for discharging the electrode mixture paste 23 to the current collector foil 2. The pump 6c is a pump that supplies the electrode mixture paste 23 from the tank 6d to the die coater 6b. The tank 6 d is a container that stores the electrode mixture paste 23.

  When the mixture paste applying means 6 is operated, the electrode mixture paste 23 stored in the tank 6d is first sucked up by the pump 6c. Then, the electrode mixture paste 23 is supplied from the pump 6c to the die coater 6b, and is supplied to one side surface (surface) of the current collector foil 2 supported by the backup roll 6a through the discharge port of the die coater 6b. In the mixture paste application means 6, the electrode mixture paste 23 is supplied over the powder molding layer 110 formed on the current collector foil 2 by the powder molding device 5. In the die coater 6b, the electrode mixture paste 23 can be continuously applied to the current collector foil 2 moving along the outer peripheral surface of the backup roll 6a.

  The current collector foil 2 to which the electrode mixture paste 23 is applied by the mixture paste application unit 6 is conveyed in the downstream direction of the mixture paste application unit 6 indicated by an arrow, and is introduced into the drying furnace 15. The current collector foil 2 coated with the electrode mixture paste 23 enters the inside of the drying furnace 15 from the inlet of the drying furnace 15. The drying furnace 15 can dry the electrode mixture paste 23 by evaporating the solvent in the electrode mixture paste 23 by blowing hot air against the current collector foil 2 coated with the electrode mixture paste 23. .

[Spray dryer]
A spray drying apparatus (not shown) is a granulated particle by spray drying an electrode mixture paste prepared using an electrode mixture component containing an electrode active material, a conductive material, a binder, and the like and a solvent for dispersing the component. It is a device for obtaining. Examples of such a spray drying apparatus include a spray dryer that performs spray drying by a spray drying method. If a spray dryer is used, the electrode mixture paste is sprayed in the form of fine particle droplets, which are brought into contact with hot air to instantaneously dry to obtain granulated particles 21.

  Next, the manufacturing method of the electrode for secondary batteries which concerns on one Embodiment of this invention using the manufacturing apparatus 1 mentioned above is demonstrated.

[Method for producing secondary battery electrode]
In the method for manufacturing an electrode for a secondary battery according to the present embodiment, a powder molding comprising a binder layer 100 made of a binder 20 on the current collector foil 2 and granulated particles 21 formed on the binder layer 100 is performed. This is a manufacturing method for manufacturing a sheet-like electrode having a layer 110 and a mixture paste layer 120 formed by applying and drying a paste-like electrode mixture containing an electrode active material and a binder on the powder molding layer 110. . As shown in FIG. 3, the method for manufacturing the secondary battery electrode mainly includes a binder coating step S10, a powder molding step S20, a mixture paste coating step S30, and a drying step S40, which are performed in this order. . The manufacturing method of the secondary battery electrode according to the present embodiment is performed using the manufacturing apparatus 1. When the secondary battery electrode is manufactured using the manufacturing apparatus 1, the manufacturing apparatus 1 includes the manufacturing apparatus 1. It is necessary to prepare the granulated particles 21 and the electrode mixture paste 23 to be supplied in advance. Therefore, first, a granulated particle preparation step and an electrode mixture paste preparation step will be described as preparation steps in the method for manufacturing a secondary battery electrode. Below, each said process is demonstrated concretely.

  The granulated particle preparation step includes a paste preparation step and a granulation step.

  The paste production process produces an electrode mixture paste at a predetermined composition ratio and solid content ratio using an electrode mixture component containing an electrode active material, a conductive material, a binder (binder), and the like and a solvent for dispersing the component. It is a process to do.

  As the solvent for dispersion, organic solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA) and water (purified water, etc.) can be used.

The granulation step is a step of granulating the granulated particles 21 using the electrode mixture paste obtained in the paste preparation step. Specifically, the granulation step uses a spray dryer or the like that is sprayed and heat-dried by a spray-drying method to spray and heat-dry the electrode mixture paste to obtain granulated particles. This is a step of crushing and classifying to produce a granule having properties such as a predetermined particle size and bulk density as the granulated particle 21.
In addition, the paste preparation process and granulation process mentioned above become a preparatory process for starting powder molding in powder molding process S20.
Moreover, the process of preparing the electrode mixture paste 23 used by the mixture paste application means 6 is the same process as the paste preparation process, and the description thereof is omitted.

  The binder application step S <b> 10 is a step of applying (coating) the slurry-like binder 20 to one side surface (surface) of the current collector foil 2 with a predetermined basis weight by the binder application unit 4. In the binder application step S10, as shown in FIG. 2, a binder layer (binder coat) 100 is formed on one side surface (surface) of the current collector foil 2. In the binder application step S <b> 10, the current collector foil 2 on which the slurry binder 20 is applied and the binder layer 100 is formed is then conveyed to the powder molding apparatus 5.

  In the powder molding step S20, the powder molding apparatus 5 continuously supplies the granulated particles 21 serving as a powdered electrode mixture to the current collector foil 2 transported along the transport path. This is a step of forming the powder molding layer 110 which is the lower layer in the electrode mixture layer 200 by press molding (compression molding) the current collector foil 2 supplied with the granulated particles 21. Specifically, in the powder molding step S20, a powdery electrode composite containing at least an electrode active material and a binder is superimposed on the binder 20 (binder layer 100) applied to the current collector foil 2 in the binder application step S10. After supplying and depositing the granulated particles 21 as an agent, the powder molding layer 110 made of the granulated particles 21 is formed by hot press molding this. The powder molding step S20 is a step performed using the powder molding apparatus 5 and includes a supply step, a flattening step, and a molding step.

  In the supplying step, the powdered granulated particles 21 obtained in the granulating step are supplied onto the current collector foil 2 by the powder supplying device 11 included in the powder molding device 5, and the granulated particles 21 are supplied. Is formed on the current collector foil 2 as a deposited layer.

  In the flattening step, the powdered granulated particles 21 supplied onto the current collector foil 2 by the powder supply device 11 using the squeegee 12 are flattened so that the surface is uniform, and a predetermined gap (Gap) is obtained. Is a step of forming a deposition layer of the granulated particles 21 having the same thickness dimension between the tip of the squeegee 12 and the surface of the current collector foil 2.

  In the molding step, the current collector foil 2 having a powdery deposited layer of granulated particles 21 deposited on the surface thereof is hot-pressed (heated) by a molding means 13 under predetermined hot-pressing conditions (heating temperature / pressing pressure). In this step, the powder molding layer 110 is formed thinner than the deposition layer of the granulated particles 21 by pressing in the thickness direction of the deposition layer. After completion of the molding step, the current collector foil 2 on which the powder molding layer 110 is formed as the lower layer in the electrode mixture layer 200 is then conveyed to the mixture paste application means 6.

  In the mixture paste application step S30, the electrode mixture paste is superposed on the powder molding layer 110 formed on the current collector foil 2 via the binder layer 100 in the powder molding step S20 by the mixture paste application means 6. 23 is a step of applying 23. In the mixture paste application step S <b> 30, the current collector foil 2 coated with the paste-like electrode mixture paste 23 is then conveyed to the drying furnace 15.

The drying step S40 is a step of drying the current collector foil 2 coated with the electrode mixture paste 23 in the mixture paste coating step S30 by the drying furnace 15. In this drying step, the solvent contained in the electrode mixture paste 23 is volatilized and the electrode mixture paste 23 is dried, whereby the mixture paste layer 120 is formed.
Thus, by the method for manufacturing an electrode for a secondary battery according to the present embodiment, the binder layer 100 that is the lowermost layer, the powder molding layer 110 that is the lower layer, and the upper layer in the electrode mixture layer 200 on the current collector foil 2. An electrode (electrode sheet) in which the mixture paste layer 120 is sequentially laminated is produced.

[Electrode Structure (Structure of Electrode Mixture Layer 200)]
As the electrode structure of the secondary battery electrode (structure of the electrode mixture layer 200) manufactured by the method for manufacturing the secondary battery electrode according to this embodiment described above, as shown in FIG. The electrode mixture layer 200 formed thereon is provided on the binder layer 100 corresponding to the lowermost layer of the electrode mixture layer 200 and the lower layer of the electrode mixture layer 200 (first mixture layer). And a mixture paste layer 120 provided on the powder molding layer 110 and corresponding to the upper layer (second mixture layer) of the electrode mixture layer 200. Yes.

The binder layer 100 corresponds to the lowermost layer of the electrode mixture layer 200 and is a layered portion of an electrode structure produced by applying the binder 20 on the current collector foil 2 by patterning.
The binder layer 100 is a layer provided between the current collector foil 2 and the powder molding layer 110 corresponding to the lower layer of the electrode mixture layer 200, and is a layer made of the binder 20. The binder layer 100 is a layer produced by applying (patterning application) the binder 20 in a predetermined pattern (for example, stripe shape) with a gravure coater which is the binder application means 4. The binder layer 100 is provided to ensure adhesion and conduction between the powder molding layer 110 containing the granulated particles 21 and the surface of the current collector foil 2.
In addition, although the electrode mixture layer 200 of this embodiment is a structure provided with the binder layer 100, it does not specifically limit to the structure of this embodiment. That is, the binder layer 100 may be appropriately provided as necessary, and is not an essential component in the electrode mixture layer 200.

  The powder molding layer 110 is a first mixture layer in which granulated particles 21 formed including at least an active material and a binder are deposited. That is, the powder molding layer 110 is a layered portion of an electrode structure formed on the current collector foil 2 by powder molding and corresponding to the lower layer (first mixture layer) of the electrode mixture layer 200. Here, powder molding refers to a method for producing an electrode in which granulated particles containing an active material are produced in advance, and the granulated particles are laminated on the current collector foil 2 and pressed.

The powder molding layer 110 is a layer that is provided on the current collector foil 2 via the binder layer 100 and is composed of powdered granulated particles 21 including the electrode active material and the binder 20, and the mixture paste layer 120. This is a layer produced by powder molding using granulated particles 21 which are more binder-rich. That is, the amount of the binder 20 in the powder molding layer 110 is larger than the amount of the binder 20 in the mixture paste layer 120 as an upper layer. The amount of the binder contained in the powder molding layer 110 is preferably about 1.0 to 5.0 wt%.
In the case of a negative electrode, the powder molding layer 110 is produced by producing granulated particles containing an active material, a binder, and a thickener, laminating the granulated particles on the current collector foil 2, and pressing. In the case of the positive electrode, the powder molding layer 110 is produced by producing granulated particles containing an active material, a binder, a conductive material, and a dispersant, laminating the granulated particles on the current collector foil 2, and pressing. Is done.
In addition, by setting the binder amount of the powder molding layer 110 to be larger than the binder amount of the mixture paste layer 120 as the upper layer as described above, the binder 20 is disposed near the current collector foil 2 as the electrode configuration. Since it can hold | maintain more reliably, the peeling strength between the current collection foil 2 and the electrode mixture layer 200 improves.
In the present embodiment, the binder constituting the binder layer 100 and the binder contained in the powder particles 21 used in the powder molding layer 110 are the same, but are not particularly limited, and different types of binders are used. Can also be used.

The mixture paste layer 120 is applied with an electrode mixture paste 23 formed by kneading at least an active material, a binder, and a solvent on the powder molding layer 110 that is the first mixture layer, and then dried. It is the 2nd mixture layer formed. That is, the mixture paste layer 120 has an electrode structure corresponding to the upper layer (second mixture layer) of the electrode mixture layer 200 formed by applying the paste on the upper layer of the powder molding layer 110 as the first mixture layer. It is a layered part.
The mixture paste layer 120 is formed by applying and drying an electrode mixture paste 23, which is a paste-like electrode mixture containing the electrode active material and the binder 20, on the powder molding layer 110 composed of the granulated particles 21. It is a layer formed by being pressed accordingly.
The mixture paste layer 120 is prepared by preparing a paste containing an active material, a binder, and a thickener in the case of the negative electrode, applying the paste onto the powder molding layer 110, and pressing it as necessary after drying. Is done. In the case of the positive electrode, the mixture paste layer 120 is prepared as a paste containing an active material, a binder, a conductive material, and a dispersant, and the paste is applied onto the powder molding layer 110 and dried and then pressed as necessary. It is produced by. The mixture paste layer 120 is a layer produced by applying the electrode mixture paste 23 while suppressing the amount of the binder 20 as compared with the powder molding layer 110. Further, the amount of the binder 20 in the mixture paste layer 120 is configured to be smaller than the amount of the binder 20 in the powder molding layer 110 which is the lower layer. The amount of the binder contained in the mixture paste layer 120 is preferably about 0.5 to 4.0 wt%.

  In the electrode mixture layer 200, the weight ratio (weight ratio) in the electrode mixture layer 200 in the two layers of the powder molding layer 110 as the lower layer and the mixture paste layer 120 as the upper layer is 10:90 to 90. : 10 is preferable.

  In addition, in this embodiment, although it is set as the structure provided with the binder layer 100 which hits the lowest layer as a layer structure of the electrode mixture layer 200, it does not specifically limit. The binder layer 100 is preferably provided when more binder 20 is held in the vicinity of the current collector foil 2 to ensure peel strength. Therefore, the binder layer 100 can be omitted as a layer configuration of the electrode mixture layer 200.

As described above, a secondary battery electrode having the above electrode structure (structure of the electrode mixture layer 200) can be manufactured. Next, a negative electrode (negative electrode sheet) is manufactured as an example of the secondary battery electrode using the manufacturing apparatus 1 and the spray drying apparatus described above, in accordance with the method for manufacturing the secondary battery electrode, and the negative electrode is used. The battery characteristics were evaluated. Hereinafter, the present invention will be described with reference to examples and comparative examples.
Hereinafter, the negative electrode (negative electrode sheet) will be described as an example of the secondary battery electrode according to the present embodiment, but the configuration is not particularly limited, and the configuration of the secondary battery electrode according to the present embodiment is positive electrode ( The present invention can also be applied to a positive electrode sheet).

[Example]
(Paste preparation process)
First, three types of electrode mixture components of graphite as a negative electrode active material, a binder (binder) made of styrene-butadiene copolymer (SBR), and carboxymethyl cellulose (CMC) as a thickener are predetermined. Composition ratio (the binder amount in this example is 5 wt% SBR in all electrode mixture components) and is dispersed in water as a dispersion solvent so that the solid content is 50 wt%. The mixture was kneaded using a mixer to prepare an electrode mixture paste for the granulation process.
In addition, about the electrode mixture paste 23 used by the mixture paste application | coating means 6, although the electrode mixture component and dispersion | distribution solvent of the same kind as the mixture paste produced at the said paste preparation process are used, The amount of SBR used as a binder is 1 wt%.

(Granulation process)
Next, the electrode mixture paste obtained in the paste preparation step was dried by hot air while spraying into the furnace under a predetermined furnace temperature condition by a spray drying method using a spray dryer to obtain granulated particles. . And the granulated particle 21 which has the desired average particle diameter and particle size distribution was obtained by performing the process of crushing and classifying the said granulated particle by a predetermined | prescribed appropriate means.
In addition, as a method of crushing the granulated particles, a known method such as a ball mill can be applied.

(Binder application process S10)
Next, the binder application means 4 causes the slurry-like binder 20 (in this embodiment, styrene-butadiene copolymer (SBR)) to be applied to one side surface (surface) of the current collector foil 2 with a predetermined basis weight. Application (coating) was performed.

  Next, the granulated particles 21 serving as a powdered electrode mixture are continuously supplied to the current collector foil 2 conveyed along the conveyance path by the powder molding device 5, and the granulation is performed. The current collector foil 2 supplied with the particles 21 was press-molded (compressed) to form a powder molding layer 110 as a lower layer in the electrode mixture layer 200.

(Mixture paste application process S30)
Next, the electrode mixture paste 23 was applied by the mixture paste applying means 6 so as to overlap the powder molding layer 110 formed on the current collector foil 2 via the binder layer 100.

(Drying step S40)
Next, the current collector foil 2 coated with the electrode mixture paste 23 was passed through a drying furnace 15 and dried.
Thus, by the method for manufacturing an electrode for a secondary battery according to this embodiment, the lowermost binder layer 100 and the lower layer (first mixture layer) in the electrode mixture layer 200 on the current collector foil 2. A negative electrode (negative electrode sheet) according to an example in which a powder molding layer 110 and a mixture paste layer 120 as an upper layer (second mixture layer) were sequentially laminated was produced. The basis weight of the powder molding layer 110 was produced with 80% of the target basis weight. The mix paste layer 120 was prepared with a basis weight of 20% of the target basis weight. That is, the powder molding layer 110 and the mixture paste layer 120 were prepared so that the weight ratio (weight per unit area) was 80:20. In this way, by increasing the basis weight of the powder molding layer 110 that is the first mixture layer than the mixture paste layer 120 that is the second mixture layer, the paste application amount is reduced, and the paste application can be performed. The accompanying solvent amount and drying time can be reduced.
And after adjusting the size of the electrode so that the design capacity of the battery becomes a predetermined value, the negative electrode (negative electrode sheet) according to the example and the predetermined positive electrode (positive electrode sheet) prepared in advance are made to face each other through the separator. Then, an electrode body was formed and sealed with a laminate together with an electrolytic solution, whereby a laminated cell type lithium ion secondary battery was produced, and an evaluation battery according to the example was produced.
Incidentally, the predetermined positive (positive electrode sheet), which was prepared by a known production method, the positive electrode active material (the present embodiment, lithium nickel composite oxide (LiNiO _2), lithium manganese composite oxide (LiMnO ₂ ), Cobalt lithium composite oxide (LiCoO ₂ ) ternary lithium-containing composite oxide), conductive material made of acetylene black (AB), and binder (binder) made of polyvinylidene fluoride (PVDF) 3 An electrode mixture component is mixed in a predetermined weight ratio and dispersed in a predetermined dispersion medium (N-methyl-2-pyrrolidone (NMP) in this embodiment) to prepare an electrode mixture paste, and an electrode The mixture paste was applied to a current collector foil (aluminum foil) and dried.

[Comparative Example 1 (electrode having an electrode mixture layer consisting only of mixture paste application: application electrode)]
The same electrode mixture components as in the above examples were mixed at a predetermined composition ratio and dispersed in water as a dispersion solvent so that the solid content was 50 wt%, and these were mixed using a kneading apparatus (planetary mixer). And kneaded to prepare an electrode mixture paste. This electrode mixture paste was applied onto the current collector foil 2 and dried to produce a negative electrode (negative electrode sheet) according to Comparative Example 1. The negative electrode according to Comparative Example 1 is a single layer in which the electrode mixture layer on the current collector foil 2 is formed by applying and drying an electrode mixture paste. Moreover, the negative electrode which concerns on the comparative example 1 contains the same kind and the same quantity as the negative electrode which concerns on an Example as a binder. Moreover, while using the negative electrode (negative electrode sheet) which concerns on the comparative example 1, and the positive electrode (positive electrode sheet) used by the Example, the evaluation battery which concerns on the comparative example 1 was produced in the procedure similar to the said Example.

[Comparative Example 2 (electrode having an electrode mixture layer consisting only of powder molding of granulated particles)]
The same electrode mixture components as in the above examples were mixed at a predetermined composition ratio and dispersed in water as a dispersion solvent so that the solid content was 50 wt%, and these were mixed using a kneading apparatus (planetary mixer). And kneaded to prepare an electrode mixture paste. Using this, granulated particles were produced by spray drying. The granulated particles were supplied onto the current collector foil 2 and an electrode mixture layer was formed on the current collector foil 2 by powder molding to produce a negative electrode (negative electrode sheet) according to Comparative Example 2. The negative electrode according to Comparative Example 2 is a single layer in which the electrode mixture layer on the current collector foil 2 is formed by powder molding of granulated particles. Moreover, the negative electrode which concerns on the comparative example 2 contains the same kind and the same quantity as the negative electrode which concerns on an Example as a binder. Moreover, while using the negative electrode (negative electrode sheet) which concerns on the comparative example 2, and the positive electrode (positive electrode sheet) used by the Example, the evaluation battery which concerns on the comparative example 2 was produced in the procedure similar to the said Example.
As described above, the initial IV resistance and the cycle characteristics are evaluated using the evaluation batteries according to the manufactured example and comparative examples 1 and 2.

[Evaluation of initial IV resistance]
About each said evaluation battery, the SOC (State of Charge) of each evaluation battery is 60% by carrying out constant current charge with the electric current value equivalent to 60% of initial capacity from the state after discharge at the electric current value of 1 / 5C. Prepared. In SOC 60%, the constant voltage of 1 / 3C, 1C, 3C is flowed for 5 seconds to measure the overvoltage during charging and discharging, and the average value of resistance calculated by dividing those values by the current value is the initial value DC resistance of All the operations described above were performed in an environment of 25 ° C. The result is shown in FIG. FIG. 4 shows a case where the initial IV resistance value of the evaluation battery (coating electrode) according to Comparative Example 1 is set to 100. As shown in FIG. 4, it was found that the resistance of the evaluation battery according to the example was suppressed to be lower than that of the evaluation batteries according to Comparative Examples 1 and 2. From this result, it was found that the evaluation battery according to the example has good battery performance with reduced battery resistance as compared with the evaluation batteries according to Comparative Examples 1 and 2.

[Evaluation of cycle characteristics]
Each evaluation battery was charged to 4.1 V with a constant current of 2 C at an environmental temperature of 60 °, and then discharged to 3.0 V with the same current density. This charge / discharge cycle was defined as 1 cycle, and this was repeated 200 cycles. Thereafter, the discharge capacity was measured in the same procedure as the initial capacity, and the discharge capacity after the cycle was determined. The capacity retention rate [%] was calculated by dividing the discharge capacity after the cycle by the initial capacity. In this way, a cycle test was performed for each of the evaluation batteries of Examples and Comparative Examples 1 and 2. As shown in FIG. 5, the cycle characteristics of the evaluation batteries according to the examples were better than those of the evaluation batteries according to Comparative Examples 1 and 2. When comparing Comparative Example 1 (coated electrode) and Comparative Example 2 (electrode by powder molding) in the initial IV resistance shown in FIG. 4, the resistance reduction effect can be confirmed in Comparative Example 2 (electrode by powder molding). Example 2 (electrode by powder molding) has a low capacity retention rate after the cycle test as shown in FIG. 5, and is not sufficient as battery characteristics. As described above, the evaluation battery according to the present example can improve the capacity maintenance rate to a level higher than that of each evaluation battery according to Comparative Example 1 using the coated electrode while maintaining the merit of reducing the initial IV resistance. did it.

  In the present invention, the electrode structure is a two-layer structure (the upper layer is made by paste application and the lower layer is made by powder molding). As described above, according to the present invention, by making the lower layer (first mixture layer) of the electrode mixture layer a powder molding layer, it is possible to reduce resistance by taking advantage of the electrode structure. Specifically, from the electrode structure of the powder molding layer constituting the lower layer of the electrode mixture layer, the electrolyte solution permeability, the orientation of the negative electrode active material, and the positive electrode conductive material dispersibility compared to the paste-coated single layer electrode Since it becomes favorable, it becomes possible to reduce resistance.

  In addition, by using the upper layer (second mixture layer) of the electrode mixture layer as a paste coating layer, the unevenness of the electrode surface area can be reduced (the electrode surface unevenness can be reduced) compared to the case of a powder molded single layer. Therefore, cycle characteristics are improved. Therefore, since the particle fluidity window that can be employed in the electrode material used for powder molding is widened, not only the cycle characteristics can be maintained, but also the resistance reduction effect is higher than that of the powder molded single layer.

  According to the present invention, as the composition of the electrode mixture layer, the lower layer (first mixture layer) is a powder molding layer, so that the electrolyte permeability, the negative electrode active material orientation, and the positive electrode conductive material dispersion The resistance is reduced because of the improved performance. In addition, since the upper layer (second mixture layer) is a mixture paste layer formed by paste application, electrode unevenness per unit area can be suppressed as compared with the case of a powder molded single layer. Improved characteristics. Furthermore, by increasing the basis weight by powder molding as compared with the mixture paste layer, the amount of paste applied can be reduced, and the amount of solvent and the drying time accompanying paste application can be reduced.

  The present invention is applicable to a secondary battery electrode having a current collector (current collector foil) and an electrode mixture layer (active material layer) formed on at least one side thereof.

2 Current collector foil 20 Binder 21 Granulated particles 23 Electrode mixture paste 100 Binder layer 110 Powder molding layer (first mixture layer)
120 mixture paste layer (second mixture layer)

Claims (2)

On the current collector foil, a first mixture layer in which granulated particles formed including at least an active material and a binder are deposited;
A second mixture layer formed by applying a mixture paste formed by kneading at least an active material, a binder, and a solvent to the upper layer of the first mixture layer; and drying the mixture. Secondary battery electrode. 2. The electrode for a secondary battery according to claim 1, wherein the basis weight of the first mixture layer is larger than the basis weight of the second mixture layer.

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